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United States Patent |
5,250,090
|
Vandervort
,   et al.
|
October 5, 1993
|
Separation devices
Abstract
Embodiments of this invention include devices for removing particles, such
as the fly ash from gaseous effluent produced by the combustion of
pulverized coal, comprising arrays of ceramic rods that are contained
within a housing having ingress and egress openings for the effluent. The
rods are so oriented as to create tortuous paths for the effluent and
thereby effectively render the rods in the aggregate into an impact
separator. The rods are made from material which exhibits electrical
resistance such that when the are sufficiently energized electrically, ash
accumulated thereon liquefies or otherwise looses its adhesive strength,
releasing such accumulations which then, by gravity and/or the drag forces
of the gas stream separate from the rods for subsequent collection and
removal.
Inventors:
|
Vandervort; Christian L. (Falmouth, ME);
LaHaye; Paul G. (Kennebunk, ME)
|
Assignee:
|
HPS Merrimack, Inc. (Portland, ME)
|
Appl. No.:
|
890804 |
Filed:
|
June 1, 1992 |
Current U.S. Class: |
95/272; 55/282.5; 55/435; 55/444; 55/523 |
Intern'l Class: |
B01D 046/04 |
Field of Search: |
55/80,96,97,269,523,DIG. 30
|
References Cited
U.S. Patent Documents
4053293 | Oct., 1977 | Combs | 55/269.
|
4684378 | Aug., 1987 | Bratten | 55/96.
|
4764190 | Aug., 1988 | Israelson et al. | 55/269.
|
4823549 | Apr., 1989 | Moser | 55/DIG.
|
5019142 | May., 1991 | Waschkuttis.
| |
Other References
Vandervort, "Factors Influencing Ash Particle Deposition in an Impact
Separator at High Velocities and Temperatures", pp. 1 to 13, Engineering
Foundation Conference, Mar. 10-15, 1991.
|
Primary Examiner: Hart; Charles
Attorney, Agent or Firm: Rhines; William G.
Claims
We claim:
1. A slag screen for removing slag from an slag-bearing stream of gas
comprising
a multiplicity of rods having collecting surfaces made from material which
is tolerant to the high temperature and other ambient conditions to which
they will be exposed, said rods
being arrayed so as to form an impact separator having tortuous paths for
the passage of a slag-bearing stream of gas therethrough whereby slag
entrained in said gas impinges upon and sticks to said collecting surfaces
of the rods, and
being adapted for their collection surfaces to be heated to temperatures
sufficient to cause slag accumulated on said collecting surfaces of said
rods to loose its adhesion thereto and to separate therefrom,
and energy means for heating said collection surfaces of said rods to
temperatures sufficient to cause slag accumulated on said collecting
surfaces to loose its adhesion thereto and to separate therefrom.
2. The device described in claim 1 wherein said collection surfaces of said
rods are adapted to be so heated by the inclusion in the structure of said
rods of material which is self heating upon the direct application of
electrical energy thereto, and wherein said energy means for so heating
same comprise electrical source connection means.
3. The device described in claim 2 wherein said self heating material is
ceramic material comprising said collecting surfaces.
4. The device described in claim 3 wherein said self heating material is
ceramic material comprising the rods themselves.
5. The device described in claim 1 wherein said rods comprise ceramic
material.
6. The device described in claim 2 wherein said rods comprise ceramic
material.
7. The device described in claim 5 wherein said rods are so oriented as to
form successive rows across the flow path of said ash-laden gas, in each
of which rows the constituent rods are spaced apart from each other and
each rod in each row is aligned with a space between the rods of each row
which next precedes it.
8. The device described in claim 6 wherein said rods are so oriented as to
form successive rows across the flow path of said ash-laden gas, in each
of which rows the constituent rods are spaced apart from each other and
each rod in each row is aligned with a space between the rods of each row
which next precedes it.
9. A slag screen device for removing slag from a slag bearing stream of gas
comprising
an outer housing having gas ingress and gas egress apertures in opposing
walls thereof,
a multiplicity of rods having collecting surfaces made from material which
is tolerant to the high temperature and other ambient conditions to which
they will be exposed, said rods
being arrayed within said housing so as to form an impact separator having
tortuous paths for the passage of a slag bearing stream of gas
therethrough whereby slag entrained in said gas impinges upon and sticks
to said collecting surfaces of the rods, and
being adapted for their collection surfaces to be heated to temperatures
sufficient to cause slag accumulated on said collecting surfaces of said
rods to loose its adhesion thereto and to separate therefrom,
energy means for heating said collection surfaces of said rods to
temperatures sufficient to cause slag accumulated on said collecting
surfaces to loose its adhesion to them and to separate therefrom, and
support means for supporting said rods so arrayed, said support means
being made from materials which is tolerant of the ambient conditions to
which it is exposed.
10. The device described in claim 9 wherein said collection surfaces of
said rods are adapted to be so heated by the inclusion in the structure of
said rods of material which is self heating upon the direct application of
electrical energy thereto, and wherein said energy means for so heating
same comprise electrical source connection means.
11. The device described in claim 10 wherein said self heating material is
ceramic material comprising said collecting surfaces.
12. The device described in claim 11 wherein said self heating material is
ceramic material comprising the rods themselves.
13. The device described in claim 9 wherein said rods comprise ceramic
material.
14. The device described in claim 10 wherein said rods comprise ceramic
material.
15. The device described in claim 13 wherein said rods are so oriented as
to form successive rows across the flow path of said ash-laden gas, in
each of which rows the constituent rods are spaced apart from each other
and each rod in each row is aligned with a space between the rods of each
row which next precedes it.
16. The device described in claim 14 wherein said rods are so oriented as
to form successive rows across the flow path of said ash-laden gas, in
each of which rows the constituent rods are spaced apart from each other
and each rod in each row is aligned with a space between the rods of each
row which next precedes it.
17. A method of removing slag from slag-bearing gas comprising the steps of
causing a slag-bearing stream of gas to pass through a multiplicity of rods
that have collecting surfaces made from material which is tolerant to the
high temperature and other ambient conditions to which they will be
exposed and are arrayed so as to form an impact separator having tortuous
paths for the passage of a slag-bearing stream of gas therethrough and are
adapted for their collection surfaces to be heated to temperatures
sufficient to cause slag accumulated on said collecting surfaces of rods
to loose its adhesion thereto and to separate therefrom, and
heating said rods to temperatures sufficient to cause slag accumulated on
said collecting surfaces to loose its adhesion thereto and to separate
therefrom.
18. The method described in claim 17 wherein said step of heating said rods
comprises the direct application of electrical energy to said rods which
are made from ceramic material that is self heating.
19. The method described in claim 18 wherein said step of heating said rods
occurs according to a prescribed sequence in which fewer than all of said
rods are so energized at any given time.
Description
BACKGROUND OF INVENTION
This invention relates to apparatus useful in the field of large boilers of
the type that are used by electric utilities to generate electricity and
in other industrial applications. In such uses, coal has been a
traditional and desirable fuel source economically and strategically
because of its great abundance, comparative low cost, and widespread
availability in the United States. More recently, natural gas and oil
distillates have become used as fuel sources, particularly as greater
emphasis has been placed on reducing contaminants and other unwanted
constituents from the effluent gases that are produced in quantity by such
installations when they use coal. That trend and efforts to improve the
efficiency of power plants have led to the concept of using combustion
gases directly to drive generating turbines without going through the
intermediate step of using the fuel to generate steam first. Thus
conventional generating systems use the Rankine Cycle, wherein coal is
used to generate steam which then drives the turbine generators, have been
combined with so-called direct fired Brayton Cycle systems, where a fossil
fuel heat source drives a turbine directly without the intermediate step
of steam generation, with the remaining heat in the spent gas from the
direct fired Brayton cycle being used as an energy source for the
associated Rankine cycle system. Systems having such combinations of
direct fired Brayton and "bottoming" Rankine systems are generally
referred to as Combined Cycles. While more efficient thermodynamically, a
major drawback of this approach is that currently gas turbines or direct
fired Brayton cycle systems are generally not adapted to the use of solid
fuels because of the high probability of the deposition of ash on the
blades of the turbine which occurs if solid fuels are used at normal
operating temperatures to heat directly the gas which drives the turbine.
To avoid this, comparatively expensive and strategically more critical
fuels, such as natural gas and distillate fuels, have had to be used,
since alternative approaches to the traditional methods of burning coal so
as to use it as the direct heat source in such Brayton Cycle systems have
also proved to be unsatisfactory. For example, coal gasification with
removal of the ash constituents is cost competitive only for large size
plants. Alternatively, subjecting the coal to pressurized, fluidized bed
processes produces maximum temperatures about 1750 F which is far below
the 2300 F needed to satisfy the needs of a modern gas turbine to achieve
high efficiency in the operation of the gas turbine. More recently, there
has emerged an alternative approach to heating the turbine working fluid
in which the fluid would be heated indirectly or through a heat exchanger.
Power plants of this type have been studied since the 1930's in an effort
to utilize high thermally efficient gas turbine cycles with solid ash
bearing fuels. This approach, referred to as an Externally Fired Combined
Cycle ("EFCC"), utilizes a heat exchanger as a means to transfer heat to
the gas which impels the turbine while, at the same time, isolating the
ash and other contaminants from the turbine itself. In this concept,
taken, for example in the context of turbine generator power plant, clean,
filtered air is admitted into the compressor section of an externally
fired gas turbine where it is pressurized and raised to a temperature of
about 375 degrees (C). This flow in the preferred embodiment becomes the
tube-side flow through a shell and tube heat exchanger, where the air in
the tubes is raised by transfer of energy through the tubes to a
temperature of about 1200 degrees C. (approximately) and then admitted
into the turbine section where it is expanded to drive the turbine and
generate electricity. This gas exits the turbine at about 540 degrees C.
and at a slight pressure above atmospheric, with part of it being supplied
to a solid fuel (e.g., coal) combustor, where the energy supplied by the
fuel raises the gas temperature to above 1350 degrees C. The products of
this combustion process flow through the shell side of the heat exchanger
and there become the source of heat that is imparted to the high pressure
compressor discharge air in the tubes. From the shell side of the heat
exchanger, the gas flows into the heat recovery steam generator comprised
of one or more superheaters, evaporators and economizers. As noted above,
a chief difference between the indirect approach and the earlier direct
concept is the elimination of the introduction of combusted fuel gases
containing ash into the turbine. That is, the ash and other contaminants
are kept from the turbine blades and other elements of the interior of the
turbine comprising the gas path, since the air from the EFCC which the
turbine "sees" is isolated from the combustion of the external firing by
the interposed heat exchanger.
In the earlier, indirect fired systems, operating temperatures were much
lower than those to which the technology has now evolved, so that high
temperature alloy steel air heaters could perform reliably. However,
metallic heat exchangers do not permit sufficiently high temperatures to
satisfy the requirements of today's high performance gas turbines,
particularly the so-called aircraft derivative machines that have been
developed for industrial use. The use of ceramic air heaters can
circumvent this obstacle since ceramics can endure temperatures well above
1370 C. in the chemically harsh environment produced by the combustion of
coal. The physical properties inherent to ceramic materials make tube type
heat exchangers the preferred form of such structures for such uses, and
experience has shown them to exhibit good durability. However, when so
applied, the ash build-up which occurs on the tubes progressively inhibits
their efficiency as heat exchange elements. This indicates a need for an
ash collection system "up-stream" of the heat exchanger in EFCC
installations to avoid such ash build up on the ceramic tubes.
Accordingly, it is an object of this invention to provide structures to
collect ash from a stream of gas. It is a further object of this invention
to provide such structures which are particularly adapted for use in
collecting coal ash. Yet another object of this invention is to provide
means which will satisfy one or more of the foregoing objectives that is
adapted for use in high temperature environments. Still another object of
this invention is to provide means which will satisfy one or more of the
foregoing objectives and is self-cleaning.
STATEMENT OF INVENTION
Desired objectives may be achieved through practice of this invention,
embodiments of which include a slag screen that is adapted to form part of
the flow path for an ash-laden stream of gas. The screen, positioned
within a housing having ingress and egress apertures, includes rods, tubes
or other structures having collection surfaces made from material such as
ceramic which is tolerant to the temperature and ambient conditions to
which they will be exposed. They are so arrayed as to form an impact
separator having tortuous paths for the gas passing through the housing,
whereby the inertia of ash particles causes them to resist the changes in
direction of the carrier gas stream in which they are entrained. The ash
particles, which include constituents that inherently are sticky, impinge
upon and stick to the rods. The rods are adapted to being heated, as by
comprising material which will convert applied electrical energy into
heat. When so heated, the rods cause certain constituents of the ash
accumulated thereon to soften, particularly at the interface between the
rods and the ash deposits. This weakens the adhesion of the ash
accumulations to the collection surfaces and induces spalling by which
accumulations separate from the rods. The ash accumulations, due to their
comparatively large size and weight, fall to the bottom of the duct into a
receptacle rather than being reintrained by the gas flowing through the
device. In that form, the ash residue may be gathered for subsequent
disposal.
DESCRIPTION OF DRAWINGS
This invention may be understood from the description which follows and
from the accompanying drawings in which
FIG. 1 illustrates an installation in which an embodiment of this invention
is used,
FIG. 2 illustrates in greater detail the portion of the apparatus shown in
FIG. 1 in which the embodiment of this invention is used,
FIG. 3 illustrates a cross-sectional view through line 3--3 of the
embodiment of this invention shown in FIG. 4,
FIG. 4 illustrates a cross-sectional view through line 4--4 of the
embodiment of this invention shown in FIG. 3,
FIG. 5 is a graph of particle size collection efficiency of embodiments of
this invention, and
FIG. 6 is a graph of Adhesion and Sticking Coefficients vs. Target Surface
temperatures applicable to embodiments of this invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring first to FIG. 1, there is shown a schematic drawing of a portion
of an electric power generation installation of a type known as an
"Externally-Fired Combined Cycle" ("EFCC") in which embodiments of this
invention may be used. In this design, clean, filtered air is admitted via
an inlet 12 into the compressor section 14 of an externally fired gas
turbine system 16, where it is pressurized and raised by compression to a
temperature of about 375 degrees C. This flow exits the compressor section
14 via piping 18 to pass through the tubes 20 of a shell and tube heat
exchanger 21 that preferably are made from ceramic materials. The gas in
the tubes 20 is raised to a temperature of about 1100 degrees C., and then
admitted into the turbine section 22 where it is expanded to drive
apparatus including the generator 24 to produce electricity. This gas
exits the turbine via ducts 26 at about 540 degrees C. and at a pressure
slightly above atmospheric. Part of it is supplied to a solid fuel (e.g.,
coal) combustor 28, where the energy supplied by the fuel raises the gas
temperature to above 1370 degrees C. After first having passed through a
slag screen 29 of a type which embodies this invention as hereinafter
described in greater detail, the products of this combustion flow to and
through the shell side 30 of the same heat exchanger and there become the
source of heat which is transferred to the compressor discharge air as it
flows through the tubes 20. From the shell side 30 of the heat exchanger,
the gas flows via ducts 32 into the super heater section 34 of the heat
recovery boiler 36.
FIG. 2 shows in greater detail the portion of the apparatus shown in FIG. 1
in the region between where the turbine air from the duct 26 enters the
coal combustor 28 and passes through the slag screen 29 and the heat
exchanger 21. As shown, the slag screen 29 processes all gas passing to
the ceramic heat exchanger 21. In this region, temperatures are typically
in the range of 1450 C. and the gas stream has a velocity of 90 to 400
feet per second.
The internal structure of the slag screen 29 is shown in greater detail in
FIGS. 3 and 4. It will be seen there that the slag screen 29 includes an
outer housing having a steel frame 50 filled, for thermal insulation, with
cast ceramic material 52 in which are positioned vertically stacked,
spaced-apart, horizontally oriented ceramic rods or tubes 60a, 60b, 60c .
. . 60n; 61a, 61b . . . 61n; 62a, 62b . . . 62n; . . . (etc.). These rods
or tubes are held in place by support blocks 75 that are so shaped and
positioned as to hold them by their ends in their desired locations as
shown. Thus, while the blocks 75 are more or less hexagonal in shape to
adapt them for aligned stacking with assurance they will stay in place
without any adhesive material between them, others may be shaped to serve
their respective functions, such as fitting into a support frame, lying
flat along a floor, etc. The rods and the support blocks may be made from
ceramic or other high temperature, structurally sound material, such as
silicon carbide which is preferred for the rods in particular because of
its resistance to temperature, its stability in chemically aggressive
environments, and (as is hereinafter elaborated) its ability to be heated
up by the direct application of electrical energy. It is noted that the
rods may be in the form of (solid) rods, or (hollow) tubes, and that
although square or rectangular or other cross-sectional shapes may be
used, circular, elliptical or tear-drop shaped cross sections usually are
preferred because of their improved aerodynamic properties for reasons
which will be apparent from what follows. Whichever among the various
tenable selections are made, the word "rod" as used herein is intended to
embrace any and all of them, whether solid or hollow. It should also be as
to design and material as to be heatable, whether by the direct
application of electrical or other energy or by supplementary heating
means. The axes of each of the rods comprising each vertical stack of rods
are offset horizontally with respect to those of rods in the vertical
stack next adjacent to it. The size, spacing and placement of the rods
with respect to each other are within the competence of those ordinarily
skilled in the cognizant arts in working out acceptable engineering
compromises between such considerations as close spacing and larger tube
sizes for improved collection efficiency versus higher resulting drag
forces. Other factors involved in these considerations involved in these
specifications, such as the shape of ash build-up, will also be within the
competence of those with such skills. Thus, the rods comprising the second
vertical stack shown in FIG. 3 (i.e., 61b, 63b) are about one or more tube
diameters apart from those comprising the first vertical stack (i.e., 60a,
62a, 64a). Similarly, the rods of the third vertical stack (60c, 62c, 64c)
are horizontally offset from those of the second stack). This sequence is
carried out throughout the device and thereby tortuous paths are created
through which the air is forced to flow. The effect of this arrangement is
illustrated by the lines of gas flow shown in FIGS. 3 and 4 into the
ingress opening at the bottom of the screen housing, through the arrays of
rods, and out through the egress opening in the top of the device. In that
process, the comparatively high inertia of the ash particles tends to
overcome the fluid drag forces, which are proportional to the projected
area of the particles and act to "sweep" the particles past the tubes.
Hence, the drag forces presented by the velocity of the fluid which act on
the mass of the particles may be balanced to create an impact separator in
which ash particles are propelled into and retained by intercepting
surfaces (in this case, the outer walls of sequential bar stacks) while
the rest of the gas continues through the device. Such separators are
particularly effective for removing particles from 5 or more microns in
size.
This collection/deposition effect is the result of two processes: particle
arrival and particle adhesion. Particle adhesion, in turn, may be further
subdivided into "reentrainment" and "spalling". Reentrainment refers to
the transport from the collector surfaces and into the gas stream of slag
"droplets" of substantially the same size and chemical form as the
entrained slag. Spalling refers to the release of larger, partially fused
chunks which are removed from the collector surfaces. Available evidence
indicates that the latter phenomenon is unlikely to be a factor with coal
slag that has passed the early stages of sintering on the collector
surfaces. Therefore, the more important issue to be addressed is that of
reentrainment of slag which has not yet passed the early stages of
sintering. Of course, it is to be remembered that these same phenomena
will operate as to gas passing through the shell side of the heat
exchanger previously described as they do in slag screens which embody
this invention since, structurally, they present similar environments.
Research into these phenomena has produced the concept of a "sticking
coefficient", which is defined as the probability that a particle which
impacts a collector surface will remain attached to that surface. It is
known that coal ash is a multiple compound, some elements of which soften
at lower temperatures than others. Thus, while coal ash may be said to be
inherently sticky, the degree of stickiness will vary as between different
coal lots, as well as with changes in temperature. In FIG. 6, which
illustrates the effect on such coefficients as the heat of coal ash is
progressively raised through temperatures which result in various changes
as noted in the physical state of the ash, the data given are
representative of those for the ash of Eastern Bituminous coal. FIG. 6
illustrates that some of the constituents of the ash are susceptible to
being softened at lower temperatures and to becoming progressively more
fluid as their temperature rises. FIG. 6 also includes a curve
demonstrating that the adhesion of ash material drops at a temperature
below that at which the sticking coefficient begins to drop materially. As
a result, the ash material exhibits a high sticking coefficient until
after it begins to loose its adhesion capability. In the present
invention, these phenomena are utilized to weaken the adhesion of
accumulated ash, which may be 6 to 15 cm or more thick. According to well
known principles of engineering, an amount of electrical energy may be
applied to the rods individually, in groups, simultaneously, or
sequentially, that is sufficient, given the desired time and temperature,
and electrical resistance, to bring their collection surfaces to the
desired temperature to release the ash deposits. By periodically heating
the rods to temperatures typically as high as about 1870 C. so that the
portion of ash accumulation next to the rod surfaces is softened, a kind
of spalling occurs in which the accumulations of ash loose their adhesion
to the collection surfaces and the ash falls away from the rods in clumps
rather than as reintrained ash particles. As such, they do not become
airborne or reintrained in the gas stream but, instead, drop to the bottom
of the apparatus for subsequent collection and disposal. and disposal. The
design of embodiments of this invention such as shown in FIGS. 3 and 4
takes the flow of gas into account by positioning the rods according to
known per se technology so that few or no such clumps falling away from
any given rod will land on any other rod.
It should be noted here that in addition to the comparatively high
efficiency of these devices in terms of heat utilization and recovery,
they also are environmentally correct. They collect many residue
constituents, some of which are in the form of inorganic ash and many of
which are non-homogenous and therefore difficult to accumulate. In the
embodiments of FIGS. 3 and 4, a means is shown for heating the rods of a
slag screen according to this invention. In a preferred embodiment, a
selected property of ceramic materials otherwise suitable for use in the
practice of this invention, is appropriate electrical resistance with
resulting internal heat generation upon the application thereto of
electrical energy. Thus, there is depicted electrical power leads 70, 71
affixed to the ends of rod 60c according to known per se techniques, by
which electrical power may be supplied to that rod to cause it to heat up.
Of course, similar energy supply means may be provided for each of the
other such rods in the device. In addition, or in the alternative, the
rods may be heated by the inclusion of supplementary means, such as
electrical wire resistance heating elements. It is also within the
contemplation of this invention that the rods may be composite structures,
for example, with a strength core and an outer ceramic layer to provide
the desired collection surface. By this means, the rods may be heated as
desired to the melting temperatures of the "glue" agents in the coal as
laden gas that is being processed, thus enhancing the ash collection,
retention and removal capabilities of the device. The means by which the
rod ends are held may be spring loaded, or pneumatically or hydraulically
or other wise actuated, or otherwise biased to retain its hold on them
against thermal expansion of the rods.
It has previously been mentioned that due to its structural configuration,
the exterior of the tubes in the heat exchanger 21 can, to some degree at
least, also be expected to function as an impact separator, somewhat in
the same way, if not to the same extent, as the slag screen. It should be
noted in FIG. 2 that after the ash laden gas passes through the slag
screen 29, it is allowed to slow down, with consequent reductions in
velocity (typically, 15 m/sec.-60 m/sec.). Since impact separator
efficiency is a function of particle diameter, particle density, gas
stream velocity and impact target size, the effect of this velocity
reduction on any ash particles which succeed in passing through the slag
screen is to reduce their tendency to impact the exterior of the tubes in
the heat exchanger with consequent ash build up which would render heat
transfer inefficient and block gas flow through it.
It is known that some of the larger coal ash particles may exceed 15
microns in size, and that an average size may be assumed to be about 10
microns. At this size, in the system described, the majority of ash
particles will pass directly through the slag screen and the heat
exchanger to be collected in a bag house. Thus, since the products of
combustion exit the coal combustor 28 shown in FIGS. 2 and 3 with a
relatively high velocity, small particles will be carried by the hot gas
stream into the slag screen, where particles larger than about 12 microns
will impact the slag screen rods. This value also represents the smallest
particles that will impact the heat exchanger tubes, plus an engineered
safety factor to better ensure capture of all particles within the size
range. Gas exiting the slag screen is directed to an ash collection area
38, and then, as previously described, passes through a region of lowered
velocities as a result of which the heat exchanger tubes exhibit a
markedly poorer impact collection efficiency. A few of the particles that
are over 30 microns in size and have managed to traverse the entire travel
path to that point may impact the heat exchanger tubes, but their number
is comparatively small, given the normal distribution curve of particle
sizes. As is summarized in FIG. 5, particles less than about 12 microns
may be collected in a bag house, while those above 12 microns are
substantially entirely removed by the slag screen. To the extent they are
not, they are, for the most part, simply swept around the tubes in the
heat exchanger by the accompanying flow of gas therethrough. Particles in
the size range between 12 and 30 microns are collected by the slag screen
and may be considered the "safety factor" referred to above.
From this description, it will be seen that through practice of this
invention, it is possible to utilize more effectively heat exchangers and
other devices involving the transfer of heat from gases laden with heat
softenable particles or droplets that will adhere to each other and to
their internal surfaces. Thus, it is to be understood that the embodiments
herein shown and discussed are by way of illustration and not of
limitation, and that a wide variety of embodiments may be made without
departing from the spirit or scope of this invention.
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